Technical Field
The present invention relates to a combustor having an ion transport membrane therein to produce molecular oxygen, and an adjustable swirler, which is mechanically connected at an inlet of a combustion zone of the combustor. Furthermore, the present disclosure relates to a combustion system and a process for combusting a fuel stream via the combustion system.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Syngas is widely used as a source of energy for industrial applications. A syngas stream can be produced via gasification of biofuels and fossil fuels (e.g. coal and heavy oil), or via reforming (e.g. catalytic reforming) of methane. Producing syngas via methane reforming powered by solar energy (i.e. solar methane reforming) can be a means for storing solar energy. Furthermore, using syngas as a fuel is in line with environmental policies adapted to reduce the carbon dioxide (CO2) emission rates. However, using syngas produced via solar methane reforming is challenging. For example, solar radiation varies significantly throughout a year, or even throughout a day. These variations result in a considerable effect in the conversion rates of the fossil fuels and the composition of the produced syngas. A change in the composition of the syngas may substantially affect the thermal energy (or Wobbe index) of the syngas, thus resulting in a change in heat release rate, a change in emission rate, and a change in stability of the combustor.
In order to efficiently extract the energy of a syngas stream produced via solar methane reforming, an adjustable system is needed to continuously adjust itself based on the variations of the fuel composition (i.e. syngas). On the other hand, the system should include a controller to stabilize the combustion conditions. The controller adjusts the system based on the variations in the fuel composition of the syngas stream.
To reduce the greenhouse gas emissions, several approaches have been adapted to effectively capture carbon dioxide. These approaches are either post-combustion, pre-combustion, or oxy-combustion. The prior art reference U.S. Pat. No. 7,927,568 B2 describes a capturing procedure that optimizes the CO2 cooling duty and compression power. Researchers are more interested in oxy-combustion approaches as a more promising way of recovering and capturing carbon dioxide from flue gases. In addition, oxy-combustion also serves as means of addressing other environmental concerns such as elimination of NOx emissions. The oxy-combustion involves burning a fuel in pure oxygen or a mixture of oxygen and carbon dioxide. Separation of oxygen from an oxygen-containing mixture (e.g. air) can be obtained, for example, via an ion transport membrane. The ion transport membrane provides a selective permeation of oxygen. The prior art reference US005534471A describes a superior oxygen separation rate (i.e. oxygen flux through the membrane) via a surface catalyzed ion transport membrane. Accordingly, an air stream was maintained at a temperature in the range of 700° C. and 1100° C., for an effective permeation of oxygen. The prior art reference U.S. Pat. No. 8,114,193 B2 demonstrated an effective oxygen separation from air using a plurality of ion transport membrane (ITM) modules that are arranged in series in a pressure vessel. To achieve the permeation temperature, the membrane may have been thermally coupled to the combustor. The US patent application 20140216046 A1 described an integration of ion transport membrane (ITM) oxygen separation systems with a gas turbine combustor to reduce a NOx emission during the operation of the combustor. The integration is such that oxygen directly permeates into the combustion zone of the combustor, while a non-permeated portion (oxygen depleted air) may either be premixed with the fuel and air, may be used as a diluent to control a NOx emission rate, or may be used as a coolant for combustor liner cooling. In another US patent application US 2014/0174329 A1 a means of controlling reaction temperatures of an ion transport membrane reactor is described via a thermally conductive plate. Furthermore, the patent reference U.S. Pat. No. 6,565,632 B1 related to a structural support disposed within a tubular ion transport membrane to prevent inward collapse of the membrane under excessive pressures. Additionally, the prior art reference EP 2,613,086 A2 disclosed a variable swirler assembly comprising a fixed and a movable blade to extend the operating range for gas turbines running on various fuels. Accordingly, the blade angles have to be set before running the turbine to give enough safety margins for a reliable operation. The system, as described in this reference, does not continuously adjust itself based on the variations of syngas composition. Furthermore, the system does not appear to mention the use of an ITM to produce pure oxygen for oxy-combusting a fuel.
The oxy combustion of syngas obtain from solar methane reforming provides a new route for an emission-free system. The emissions from such systems are mainly carbon dioxide and water vapor. The water vapor can be condensed and a relatively pure carbon dioxide can be captured. As a result, the costs associated with post-combustion or pre-combustion treatments to capture CO2 are either eliminated or at least substantially reduced. Having an ITM integrated to a combustor provides a continuous supply of pure oxygen for an oxy-combustion process. The oxy-combustion process is generally carried out at a relatively high temperature, and thus produces high temperature products. As a result, a recycle stream may be needed (e.g. a portion of the flue/exhaust gas) to be mixed with the fuel stream to keep the temperature of the combustion within an allowable temperature range.
The main challenge in the design of such systems is the adaptability of the system to compositional changes of the fuel. In addition, issues such as controlling the flow rate of the fuel to be in the stoichiometric ranges with the permeated oxygen, or controlling the flow rate of the recycling exhaust gas based on its temperature need to be addressed to avoid major thermal and/or mechanical stresses on the system. While an integration of an ITM combustor to a gas turbine has been disclosed in the prior art, an ITM-combustor having an adjustable swirler, which is connected to a feedback control system, for an efficient oxy-combustion does not appear to be disclosed previously.
In view of the forgoing, one objective of the present disclosure relates to a combustor having an ion transport membrane therein to produce molecular oxygen, and an adjustable swirler, which is mechanically connected at an inlet of a combustion zone of the combustor. Furthermore, the present disclosure relates to a combustion system having the combustor, a feedback control system adapted to adjust the swirler blades based on the compositional variations of a fuel stream, and a plurality of feedback control systems to control operational variables (i.e. temperature, flow rate, pressure, etc.) within the combustor for an efficient oxy-combustion. The present disclosure also relates to a process for combusting a fuel stream via the combustion system.